As one form of a cap for optical device, there is a structure obtained by joining a silicon to a borosilicate glass by anodic bonding. FIG. 3B illustrates an example of the structure, in which a frame-shaped member 18 made of silicon is joined to a peripheral portion on one surface of a plate-shaped borosilicate glass 13. Reference numeral 20 denotes an optical device (light emitting element in the illustrated example) disposed in a cavity formed by the plate-shaped member (borosilicate glass) 13 and the frame-shaped member 18.
As the art related to sealing of such an optical device, for example, there is known a light emitting device described in Patent document 1 (Japanese Laid-open Patent Publication No. 2009-170723). As another related art, there is known a semiconductor device described in Patent document 2 (Japanese National Publication of International Patent Application No. 2008-0238241)
As illustrated in FIG. 3B, in the configuration of the cap 10a for optical device according to the state of the art, the interfaces of the borosilicate glass (plate-shaped member) 13 and the silicon (frame-shaped member) 18 are covalent bonded by anodic bonding. Accordingly, the joined portion of the glass 13 and the silicon 18 is optically transparent. As a result, problems arise in that unnecessary reflection of light occurs at a portion of the glass on the joined portion and thus the optical characteristics are deteriorated. The particular of the problems will be explained in connection with the embodiments as described later.